Propylene carbonates are important intermediates in a number of different processes, for instance, as the replacement of highly toxic phosgene as carbonylating agents in processes such as the production of isocyanates or polycarbonates.
Another important use of propylene carbonates is the production of 1,2-propanediol by catalyzed hydrolysis. The propylene carbonates can also be used for the preparation of dimethyl carbonate, which has raised interest for use as octane enhancers in fuels as a replacement for methyl tert-butyl ether.
It has been found advantageous if the process can be carried out at a relatively high temperature such as of from 150 to 250° C. while the catalyst is recycled. It was found that such process makes efficient use of the starting compounds while an efficient heat-integration is possible. However, the combination of high temperature and catalyst recycle requires the catalyst to be very stable.
U.S. Pat. No. 5,153,333 describes a process for the conversion of epoxy resins at a temperature of from 60 to 160° C. with the help of quaternary phosphonium compounds. The catalyst remains in the final product in the exemplified process.
Phosphoniumbromide catalysts are mentioned in prior art such as U.S. Pat. No. 2,994,705, U.S. Pat. No. 4,434,105, WO-A-99/57108 and EP-A-776,890. However, there is no teaching in any of these documents on what catalyst is to be used if the propylene carbonate manufacture is to be carried out a temperature of from 150 to 250° C. and with recycle of the catalyst.